Department of Electrical Engineering University of North Texas

Transcription

1 Name: Shabuktagin Photon Khan UNT ID: Instructor s Name: Professor Hualiang Zhang Course Name: Antenna Theory and Design Course ID: EENG khan.photon@gmail.com Department of Electrical Engineering University of North Texas

2 Contents Abstract... 1 Technical Method... 1 Microstrip... 1 HyperLynx... 2 Flow Chart of the HyperLynx... 3 The General Dimension of the Microstrip Antenna... 3 Feeding Structures of Microstrip Antennas Equivalent Circuit... 4 Structure and Methods... 5 S-Parameter... 7 Gain, Directivity and Radiation Efficiency Conclusion and Further Discussion Problems Faced Final Thoughts References... 15

3 Abstract In this lab, LineGauge was used to design a rectangular patch microstrip antenna with a center frequency of 2.3 GHz. The substrate is RT/Duroid 5880 which has a dielectric constant of 2.2. The substrate thickness is mm with a lost tangent = At the end, S-parameter simulation and plotting the radiation parameters of the rectangular patch was done using slots and without slots. Technical Method Microstrip A microstrip is a thin, flat electrical conductor separated from a ground plane by a layer of dielectric or an air gap. The characteristic impedance (Zc) of the Microstrip-Line is determined by W, d, and the permittivity of the substrate. Figure 1(a): Microstrip Microstrip is a type of electrical transmission line which can be fabricated using printed circuit board technology, and is used to convey microwave-frequency signals. It consists of a conducting strip separated from a ground plane by a dielectric layer known as the substrate. Microwave components such as antennas, couplers, filters, power dividers etc. can be formed from microstrip, the entire device existing as the pattern of metallization on the substrate. Microstrip is thus much less expensive than traditional waveguide technology, as well as being far lighter and more compact. The EM wave that travels along the microstrip exists partly in the dielectric substrate, and partly in the air. This means the wave is traveling in an inhomogeneous medium (different phase velocities). Figure 1(b): Electromagnetic Wave in Microstrip

4 2 Antenna Theory and Design In one homogenous medium, so the term effective dielectric constant was introduced. We then treat the EM wave as a quasi-tem wave (a hybrid of TE and TM modes). The characteristic impedance Zo of a microstrip is determined by the width of the strip, the thickness of the substrate and the dielectric constant of the substrate. HyperLynx also provides a way to calculate the characteristic impedance of a microstrip in LineGauge HyperLynx HyperLynx is a powerful electromagnetic simulation software. It numerically solves the Maxwell s equations with suitable boundary conditions. It is commonly used among the RF/microwave engineers. Types of simulation in HyperLynx S-Parameter Simulator Antenna Characteristics Simulations Including Radiation Pattern, Gain etc. LineGauge: Analyze and synthesize different types of transmission line structures S-parameter simulation is used for as following Multi-port frequency domain simulation. Most commonly used to characterize passive and active RF/microwave components: filters, matching network, LNA, etc.

5 Flow Chart of the HyperLynx Figure 2: Flow Chart of the HyperLynx The General Dimension of the Microstrip Antenna

6 4 Antenna Theory and Design Using the same concept and the equations, the length and width of the microstrip patch is calculated. W = V 0 (2f r ) 2 ε r + 1 = /( ) = m = 5.156cm = 5.2cm = 52 mm 2. (2.3G) ε reff = ε r ε r 1 [1 + 12h w ] = ΔL h = (ε W reff + 0.3) ( h ) (ε reff 0.258) ( W = h + 0.8) ΔL = (0.529) = mm L = λ 2ΔL = 43.6 mm [ ] = 2.15 ( ) ( ) ( ) ( ) = Feeding Structures of Microstrip Antennas Equivalent Circuit Figure 3: Microstrip Feed line and the Equivalent Circuit The characteristics of Microstrip Feed are listed below: Easy to fabricate Simple to match Low spurious radiation at around -20dB Narrow bandwidth (2-5%) The Spurious feed radiation increases as the height of the substrate increases

7 Structure and Methods The following steps below were done to get the length and width of the microstrip line. Step 1: Start Line Gauge from Hyperlynx program manager Step 2: Input Parameters of Microstrip-Lines Step 3: Do the calculation by click Electrical to Physical (Quarter wavelength) Figure 4: Line Gauge for Microstrip New Project was created using M-Grid which was selected from Hyperlynx program manager. The following steps below were done. 1. On the main window of the Layout Editor, the icon file was clicked and new icon was selected. 2. Then the window called Basic Parameters popped up 3. The material property was filled using the required values which is shown in figure 5.

8 6 Antenna Theory and Design Figure 5: Defining the Substrate Layer (Material Property) The layout was drawn by using Rectangle entity. The length of the rectangular patch is 43.6 mm and its corresponding width is 52 mm. The length and width of the transmission line is taken from line gauge which is approximately mm in length and mm in width. Figure 6: Rectangular patch with transmission line

9 S-Parameter The simulation was setup to S-Parameter which are shown in figure 7 and figure 8. S-Parameters are Scattering Parameters which are defined to represent the voltage ratios between different ports Following steps below were followed to setup S-parameter Simulation Setup simulation port. Setup simulation frequency range. Plot simulation results. Figure 7: Scattering Properties Figure 8: Frequency Range

10 8 Antenna Theory and Design Figure 9: Simulation Graph: Microstrip Patch The equation below was used to find the original value of the reflection 20log 10 (non db value) = (db value) non db value = 10 db value 20 Therefore, the non-db value is The designed antenna almost resonates at 2.3 GHz. The S 11 = -5.5dB is not well matched. Therefore, the impedance matching needs to be improved by creating a slot. Therefore, S 11 needs to be nearby -20dB (non-db value = 0.1). The new rectangular patch with a slot is shown below with the simulation graph.

11 The option for the cut the polygon from the selected edge was chosen and the cut width and length values are shown in Figure 10. Figure 10: Cut the Polygon from the selected edges Figure 11: Microstrip Patch with slot Figure 12: Simulation Graph: Microstrip Patch S 11 is nearby db

12 10 Antenna Theory and Design The graphs related to the simulation are shown below: Figure 13: 3D radiation pattern This equation measures the peak value of radiated power divided by the average, which gives the directivity of the antenna. The typical directivity of the patch microstrip antenna ( ) / (5-8 db) More the directivity more the focused or directional the antenna is. Even though there is no isotropic antenna in real life but it is used as a common reference.

13 Figure 14: Azimuthal Pattern Directivity Display Figure 15: Elevation Pattern Directivity Display

14 12 Antenna Theory and Design Figure 16: Total Gain versus Frequency Display From the graph it can be deduced that the total gain is around 4.8dBi at 2.31 GHz but the highest total gain is approximately 5dBi in between 2.25 to 2.31 frequency range. Figure 17: Total Field Directivity versus Frequency Graph The total directivity is highest at 2.5 GHz which is around 7.6dBi but for 2.31GHz it is 7.55dBi

15 Figure 18: Directivity vs Elevation Angle The total directivity for 2.31 GHz at 0 degree elevation angle is 7.55 dbi Figure 19: Directivity vs Azimuth angle

16 14 Antenna Theory and Design Gain, Directivity and Radiation Efficiency G = 4. 8 dbi D = dbi e r = ( )( 1) = dbi Therefore, the radiation efficiency = which is 53 % Conclusion and Further Discussion Problems Faced The calculations could have been more accurate if the approximate values were not taken. Also, the center frequency moves from 2.3 GHz to 2.31GHz when the slot was implied to the rectangular patch. For calculation for radiation efficiency, it gives the positive db but that positive value was changed to negative value. Final Thoughts This lab helped us to get familiar with the Hyperlynx software. It would further help us to understand the Antenna Theory concepts and calculation inside the transmission line.

17 References [1] [2] Rao, Nannapaneni Narayana. Fundamentals of Electromagnetics for Electrical and Computer Engineering. Upper Saddle River, NJ: Pearson Prentice Hall, Print. [3] Balanis, Constantine A. Antenna Theory: Analysis and Design. 3rd ed. Hoboken, NJ: Wiley Interscience, Print.